Variable vane cascades

ABSTRACT

A TURBINE NOZZLE INCLUDES AN ANNULAR ROW OF RADIALLY DIRECTED BLADES. THE AREA OF THE NOZZLE THROAT IS VARIED BY PLUTS WHICH ARE MOVABLE WITH OR AGAINST THE DIRECTION OF FLOW THROUGH THE NOZZLE INTO THE SPACES BETWEEN THE BLADES. THE PLUGS ARE STREAMLINED MEMBERS AND MAY BE INDIVIDUAL MEMBERS IN EACH INTERBLADE PATH OR MAY BE PORTIONS OF A RING EXTENDING AROUND THE NOZZLE AXIS IMMEDIATELY DOWNSTREAM OF THE NOZZLE. PROVISIONS ARE MADE FOR COOLING THE PLUGS.

3,567,331 VARIABLE VANE CASCADES Leo A. Corrigan and Earle R. Wall, Jr.,Indianapolis, Ind., assignors to General Motors Corporation, Detroit,

Mich.

Filed July 25, 1969, Ser. No. 844,885 Int. Cl. F01d 25 24, 17/00 U.S.Cl. 415-126 7 Claims ABSTRACT OF THE DISCLOSURE A turbine nozzleincludes an annular row of radially directed blades. The area of thenozzle throat is varied by plugs which are movable with or against thedirection of flow through the nozzle into the spaces between the blades.The plugs are streamlined members and may be individual members in eachinterblade path or may be portions of a ring extending around the nozzleaxis immediately downstream of the nozzle. Provisions are made forcooling the plugs.

The invention herein described was made in the course of work under acontract or subcontract thereunder with the Department of Defense.

Our invention is directed to variable vane cascades suitable for use asstator vane rings in turbomachines such as compressors and turbines, andfor other uses. It is also directed to means for cooling the structureso that it is suited for use in very high temperature turbines. In astructure according to our invention, the turbine nozzle includes a ringof fixed vanes defining between them paths for flow of gas, each pathhaving a throat between the trailing edge of one vane and the adjacentvane. To vary the area of the nozzle, a plug is moved within the throatvarying the throat area by virtue of the variation of plug cross sectionarea at the throat. There may be an individual plug between each twoadjacent vanes or there may be a continuous ring, the portions of whichbetween vanes each constitute a plug.

The principal objects of our invention are to provide a practicalvariable vane cascade structure; to provide a variable vane cascade inwhich the variation is accomplished by movement of a ring of plugsextending generally circumferentially of the nozzle into the spacesbetween the vanes; to provide a structure of the kind described in whichthe plug structure has provisions for cooling; and to provide a variablearea vane cascade having simple reliable structure particularly adaptedto the requirements of practice.

The nature of our invention and its advantages will be clear to thoseskilled in the art from the succeeding detailed description of preferredembodiments of the invention and the accompanying drawings thereof.

FIG. 1 is a sectional view of a variable turbine nozzle taken in a planecontaining the axis of rotation of the turbine and with parts brokenaway and in section.

FIG. 2 is an axonometric view of a nozzle throttling plug.

FIG. 3 is an axonometric view of a nozzle throttling plug ring.

FIG. 4 is a schematic view illustrating the movement of the plugs.

Before proceeding to a description of the structure in which ourinvention is particularly embodied, it is well to point out that thestructure, except as otherwise described, may be of a type shown incopending applications, of common ownership with this, of Earle R. Wallfor Variable Turbine Nozzles, Ser. No. 836,423, filed June 25, 1969, andfor Variable Vane Cascades, Ser. No. 836,422, filed June 25, 1969. Tothe extent that United States Patent 3,567,331 Patented Mar. 2, 1971structures disclosed herein correspond to those of the priorapplications, they may not be described in detail; however, We believethat all structure is described here to the extent requisite to a fullunderstanding of our invention. Reference may be made, if needed, to theprior applications for details described therein.

Referring first to FIG. 1, this illustrates a variable nozzle or statorring for an axial flow turbine, which may be of various known types. Theturbine includes a case 5 to which is fixed the outer shroud ring '6.The turbine also includes a support 7 within the engine which is fixedby means not illustrated to the turbine case 5. An inner shroud ringassembly 8 is fixed to the support 7. Fluid flow directing vanes 10disposed in an annular array extend radially from the outer shroud 6 tothe inner shroud 8.

The outer shroud ring 6 includes a structural ring 11 including a flange'12 fixed to the case 5 by a ring of bolts 13. The outer shroud alsoincludes a porous facing defined by an upstream facing ring 14 and adownstream facing ring 15, the former being fixed to the structural ring11 by bolts 16 and the latter being secured by a snap ring 18. The innershroud ring 8 includes an inner structural ring 19 having a flange fixedto the support 7 by suitable means (not illustrated). It also includesan upstream porous facing ring 20 and a downstream porous facing ring22, these being held in place on the structural ring 19 by rings 23which snap into place, this structure being part of the subject matterof the Wall applications. The division of the porous facings intoupstream and downstream rings provides for mounting them around thevanes 10.

Each vane 10 includes an airfoil 24 which defines the leading edge,face, and trailing edge of the van, the trailing edge being indicated at25. The airfoil 24 is fixed to a tubular spine 26 which extends to thestructural rings 11 and 19 and supports the vane from them. Spine 26 isslidably mounted in a bore 27 in a flange of the inner structural ring19 and is fixed to the outer structural ring 11, the outer end of thespine extending through a hole 28 in the ring and being retained by acontracting snap ring 29. The vane bears flanges 30 at its ends whichextend over the outer and inner surfaces of the facing rings to minimizeleakage of cooling air between the facings and the vane.

Air for cooling the shrouds and vanes may enter the outer shroud throughopenings 36 and the inner shroud through openings 37 and may flow intothe vane through the open ends of the vane and also into the spine 26through open ends of the spine. The structure of the cooling means ofthe shrouds and vanes is immaterial to this invention.

Our invention is directed to the means for varying the flow area of thenozzle or area of the nozzle throat which involves plugs 40 (FIG. 1)movable in the direction of fluid fio'w into or away from the nozzlethroat adjacent the trailing edge of one vane and the approximatemid-chord of an adjacent vane. The plug means 40 may take either of theforms shown in FIGS. 2 and 3.

The device of FIG. 2 is a short airfoil 41 normally of symmetricalsection with a leading edge at 42 and a trailing edge at 43. The ends ofthe airfoil 41 are closed by caps 45. The structure of the plug means 40is of porous material so that cooling air introduced to the interior ofthe plug means can diffuse through the entire outer surface fortranspiration cooling.

The plug means 40 of FIG. 3 is defined by a ring airfoil 48 having asimilar cross section to the airfoil 41. The ring may be a single 360ring extending around the turbine nozzle or it may be in sections orsegments if desired. The ring airfoil 48 has a notch 49 at the positionof each vane defined by radial walls 50. The surfaces of the ringairfoil 48 likewise are of porous material for transpiration cooling.

Referring to FIG. 1, the plug means is supported by hollow struts 51, ofstreamlined cross section to minimize resistance to air flow, therebeing one strut 51 for each airfoil 41 and a suitable number of struts51 for the ring airfoil 48. The struts 51 are integral with a mountingand actuating ring 54 of rectangular cross section which is mountedbetween the support ring 11 and downstream facing ring 15 and supportedby these so that it may slide forward and aft in the structure and alsomove circumferentially to a slight extent. The strut 51 extends througha skewed slot 55 in the facing ring '15 and the actuating ring 54 coversit. An offset connecting bracket 56 includes a head 57 welded to thering 54 and terminates in a pin 59 which connects it to an actuating arm60.

An appropriate number of actuating arms 60 may be distributed evenlyaround the circumference of the nozzle, each such arm being pivoted at61 on a flange of the structural ring 11 and having mounted in it aspherical bearing device 62 which receives the pin 59. The arms 60 maybe rotated in unison by a unison ring 64 coaxial with the turbine anddisposed within the case 5, which is connected to the arms 60 throughspherical bearings 65. Brackets 56 extend through skewed slots 66 in thestructural ring 11.

The nature of the movement of the plug means will be clearly apparentfrom the somewhat schematic showing in FIG. 4. As the arm 60 is swung inthe are indicated by the arrow A, the plug means 40 is moved in acorresponding are indicated by the arrow B, and is thus moved to agreater or lesser extent into the throat between the adjacent vanes 10.It will be noted that the intermediate connecting means between the pin59 and the plug means are not illustrated in FIG. 4.

The plug means 41 move together as a unit although each is a separatepart. The ring 48 moves as a unit and has a suflicient number of struts51 connecting it to the mounting and actuating ring 54 to providesuitable support and conduct sutficient cooling air to it.

The cooling air which is admitted through holes 36 to the interior ofthe shroud 6 flows in part through a ring of holes '68 in the leadingedge of the ring 54, through the hollow struts 51, and into the chamber70 within the plug means. Since the walls of the plug means (includingwalls 45 in FIG. 2) are a suitable temperature resisting alloy and havea controlled degree of porosity, the air transpires through the plugsurface to cool the plug and protect 'it against the hot gasesdischarged through the turbine nozzle.

It will be apparent to those skilled in the art that our inventionprovides means for varying to a limited extent the area'of a turbinenozzle for various purposes of engine control known to those skilled inthe art. The structure is of a simple and feasible nature and isparticularly suited to hot environments because of the provisions forcooling.

- The detailed description of preferred embodiments of the invention forthe purpose of explaining the principles thereof is not to be consideredas limiting or restricting the invention, since many modifications maybe made by the exercise of skill in the art. We claim:

1. A turbomachine structure comprising, in combination, an annularsupport, an annular cascade of fixed flow directing vanes extendingspanwise of the vanes from the support, the vanes defining a fluid flowpath through each space between adjacent vanes, area-varying plugsdisposed between adjacent vanes, and means mounting the plugs forconcurrent movement in the direction of flow through the said pathstoward and from the entrance to said paths so as to vary the flow paththroat area, the plugs being airfoil structures with span extendingcircumferentially of the vane cascade.

2. A structure as defined in claim '1 in which the mounting meansincludes a ring movably mounted on the support.

3. A structure as defined in claim 2 including streamlined strutsextending from the ring to the plugs.

4. A structure as defined in claim 2 in which the plugs are defined by adistinct plug between each two adjacent vanes, each plug beingindividually connected to the ring.

5. A structure as defined in claim 2 in which the plugs are defined bya'ring airfoil having notches to References Cited UNITED STATES PATENTS2,372,518 3/1945 Robinson 415148 3,249,333 5/1966 Corbett, Ir. 4l51613,433,015 3/1969 Sneeden 4l6-231 HENRY F. RADUAZO, Primary Examiner U.S.Cl. X.R. 415l15,148,

